Domino Hydroalkoxylation‐[4+2]‐Cycloaddition for Stereoselective Synthesis of 1,4‐Heterocycle‐Fused Chromenes: Rapid Access to the [6‐6‐7‐6] Tetracyclic Core of Cytorhizhins B–D

Abstract

A substrate dependent regio‐ and stereoselective domino hydroalkoxylation‐formal‐[4+2] cycloaddition is described for the facile synthesis of linear as well as spirocyclic 1,4‐heterocycle‐fused chromene ketals. Enantiospecific synthesis of oxazepino chromene derivatives was successfully carried out using chiral pool amino alkynols. The developed hydroalkoxylation cascade offered rapid access to the spirocyclic [6‐6‐7‐6] tetracyclic core of cytorhizhins B–D with correct relative configuration.